WO 01/63554 A2 and US 2003/0107832 A1 teach a marking device for the identification of objects. A carrier film made of polyester is firstly vapour-deposited with a first layer made of NiO and subsequently with a second layer made of NiFe. The marking may be used, instead of a magnetic strip, on cheque cards, credit cards, access cards, electronic keys or the like for checking authenticity.
From A. Ehresmann et al., “On the origin of ion bombardment induced Exchange Bias modifications in polycrystalline layers” 2005, J. Phys. D. 38, 801, there is known a multilayer system having a plurality of magnetic layers arranged one upon another which comprises a ferromagnetic layer having a large number of biased domains with asymmetrical remagnetisation properties.
U.S. Pat. No. 4,960,651 discloses magnetic elements containing an object which has a substrate and a thin coating with an amorphous magnetic material. The object can be used as an anti-theft marking.
From DE 196 04 746 A1 there is known a security element for electronic article protection. It solves the problem of modifying a known security element, composed of a plurality of magnetic materials, such that it is detected by a harmonic detection system. This is done by providing a material with a high Barkhausen effect, which is arranged relative to a soft magnetic material in such a way that the two can be coupled to one another via their stray fields, and by providing a medium-hard or hard magnetic material which biases the material with the high Barkhausen effect.
CA 2 451 548 discloses an authenticity feature, in particular a security thread for banknotes, which has optical, electronic and magnetic security features. The security features are applied in a manner overlapping in layers and cannot be optically distinguished from one another. The magnetic security feature can be applied by magnetic ink, and individual regions forming the magnetic security element may differ in their magnetic remanence or in their coercive field strength. The different types of magnetic regions can therefore be distinguished in identifying machines through their different magnetic properties. The different magnetic properties of the regions may be caused by different magnetic materials, by varying the amount of material and/or the pigment distribution, the term pigment distribution referring, for example, to the pigment size or the density distribution of the pigments. As materials, hard and soft magnetic materials are equally suitable.
From US 2008/0193639 A1 there is known a method for marking composite materials. A marking is applied by means of magnetically doped ink between layers of the composite material. The marking can be read by suitable reading devices for magnetic markings, although it is located between two layers of the composite material and is thus invisible or at least hidden to the eye.
U.S. Pat. No. 7,159,779 B2 discloses a barcode scanning machine with at least two cameras. The at least two cameras scan one after the other a barcode of sheets guided past them. A controller receives signals from the first and from the second barcode scanner and interprets them by means of a predetermined algorithm. The algorithm can be selected, so that different levels of reliability checking are provided.
From DE 600 03 067 T2 there is known a security system for the protection of various articles, and a method for reading a code marking. A main feature of the invention is to provide an appropriate system comprising a magnetic read-only pattern with a high density which is not visible to an individual's eyes and has a reading head suitable for reading this pattern. In addition, another feature of the invention is to provide a reading head which is designed to be adapted to the unique response characteristics of the material of the code pattern. The reading head is provided with magnetic means, so that an effective response of the reading head occurs only in a narrow zone. The magnetic elements are preferably glass-coated microwires made of a soft magnetic material having a very low remanence. The density of the microwire pattern is considerably higher than that which is obtained with known magnetic materials such as magnetic inks. The code patterns formed by the microwires cannot be read with known readers, because the sensing range of known readers is much larger than the distance between the microwire pieces.
DE 103 14 631 A1 discloses a plane sheet material with individual information. The sheet material or the sheet has magnetisable particles, and individual information is incorporated in the sheet material. Substantially unchangeable individual information is stored on the sheet material by the manufacturer by means of the magnetisable particles, and moreover incorporated in the sheet in encrypted form as check information. The individual information and the corresponding check information can be checked for a match using only a corresponding key. The storing of the individual information can be carried out such that while being easily readable it is substantially unchangeable in content, which increases the degree of security against counterfeiting. A suitable testing device comprises decryption software which enables detection of the match between individual and check information.